Cutter support and cutter head

ABSTRACT

The invention relates to a cutter support for fixing in a cutter head, comprising a shaft-like bar and a head with integrated cutters with minor cutters formed from a cutting surface and a free surface. According to the invention, a chamfer adjacent to the minor cutter is arranged on the free surface with a chamfer width decreasing outwardly to 0.

The invention relates to a blade holder for fixing in a milling head,comprising a shaft-like bar and a head having blades attached bysoldering and having a lateral cutting edge formed by a cutting face andan open face.

The invention further relates to a milling head having several bladeholders placed in seats in a base body, with blades being soldered ontoeach of the blade holders, the blade holders each being axiallydisplaceable via a wedge and fixable in the milling head by means ofclamping elements.

The milling head is known in principle from DE 40 03 862. In the millinghead described there, the seats for the blade holders extend from theface of its base body parallel to its rotational axis as well as spacinginward from its outer periphery, with the blades of the cutting platesused protruding only slightly past the face of the base body. Moreover,the axes of the round wedges used for gripping each extend at a smallacute angle to the cutting-plate holder. Finally, a additional roundwedge with a differential screw is also provided for the axialadjustment of each cutting plate and set in a respective seat thatextends radially inward from the outer surface of the base body.Geometrically identical round wedges are used for axial adjustment andclamping directed radially outward. As an advantage of this millinghead, the document emphasizes the fact that, due to the position of theseats accommodating the cutting-plate holders parallel to the rotationalaxis of the base body, only radially oriented centrifugal forces occurwithout axial components. These forces may be easily absorbed becausethe seats are not located directly on the outer surface of the basebody; rather they are located radially inward at a distance from theouter surface. Therefore, the milling head is also suitable forextremely high rotational speeds and the centrifugal forces that occurat such speeds. It is advantageous for a fine adjustment of the millingelements to be possible axially without overlapping with radialcomponents.

While according to the prior art crankshafts for motor vehicles aresubjected to a finishing process by grinding or belt grinding, themilling being performed using cooling lubricants, by virtue of theprocess with the development of suitable milling tools it becamepossible for grinding of crankshafts to be replaced by milling. Due tothe structure of the crankshafts, orthogonal lathe milling is used withan eccentric tool position without axial advance. Here, the toolperforms a plunge motion on the basis of which the design of the bearingseats is exclusively produced by the lateral cutting edge of the tool.Here, the tool must be positioned relative to the workpiece in such away as to ensure that, on engagement of the lateral cutting edge, theentire crown line of the bearing seat is covered. The bearing seatdiameter to be produced is generated via this crown line. By virtue ofthe process, the central regions of the lateral cutting edge is longerin engagement than other regions. This causes the blade to have agreater degree of wear in the central region than in the outer regions.

Additional details regarding orthogonal lathe milling may be found, forexample, in DE 10 2004 022 360 A1. However, orthogonal lathe millingwith an eccentric tool position without axial advance has a decisivedisadvantage. By virtue of the fact that, in this method, the lateralcutting edge of the tool performs a plunge operation, the smallesterrors in cutting or tool wear have an immediate negative effect on theform and surface quality to be achieved. The unevenly distributed toolwear in particular leads to early deviations in shape.

The object of the present invention is to eliminate the disadvantagesmentioned above; in particular, a cutting shape should be found that atthe same time guarantees workpiece processing in a precise shape inaddition to as long a useful life as possible.

The further object of the present invention is to provide an appropriatemilling head for this purpose.

The first object mentioned above is attained by a blade holder accordingto claim 1. According to the invention, the blade holder has a beveladjacent the lateral cutting edge and formed on the free face, having abevel width decreasing outward to 0. Additional embodiments of the bladeholder are described in the subclaims.

The object is further achieved by a milling head according to claim thatis characterized by three blade holders that are set at an equidistantangle to one another.

In the blade holders known from the prior art without the bevelaccording to the invention, a high level of initial wear resulted in thecenter of the blade, namely at the point where the blade has the longestcontact time with the workpiece. In contrast, regions located on theedges with a substantially shorter cutting engagement showed a lowerdegree of wear on the free faces. When the blade holder according to theinvention was used, on the other hand, it was possible to significantlydecrease the tapered wear region with a high degree of initial free facewear, such that it was possible to correspondingly lengthen the regionin which the free face wear occurred in a linear fashion.

Additional details of the invention shall be explained with reference tothe figures, in which:

FIG. 1 is a perspective view of a milling head with three blade holders,

FIG. 2 shows a wire-frame view of the milling head according to FIG. 1,

FIG. 3 is a longitudinal section through a milling head without bladeholders,

FIG. 4 is a side view of a blade holder,

FIG. 5 is a view of the relative position of a blade holder to a clampbody and a wedge for axial adjustment,

FIG. 6 is an additional side view of the blade holder,

FIG. 7 is a large-scale sectional view of the region marked “A,”

FIGS. 8 and 9 are large-scale views of the blades according to FIG. 4 intwo different embodiments,

FIG. 10 is a top view of the free face of a blade, and

FIG. 11 is a schematic wear curve.

The milling head shown in FIGS. 1 to 3 is comprised essentially of abase body 10 for three blade holders 11 onto which having respectiveblades 12 are brazed. The blade holders 11 are mounted in respectivebores 22 (see FIG. 3) extending parallel to a longitudinal axis 13.Three additional bores are provided in the base body 10 extendingessentially radially or at a small acute angle to a radius and holdingrespective wedges 14 that are displaceable radially via respectiveadjustment screws 15, preferably double-thread screws.

As may be seen from FIG. 5, the wedges 14 have wedge faces 16 extendingat an acute angle to a radial plane of the base body such that, onradial movement of the wedge 14, the respective blade holder 11 is movedalong its longitudinal axis, i.e. axially. A clamp body 18 is used forclamping the blade holder, the clamp body being centrally positioned andhaving three clamping faces 19 fitting against complementary clampingfaces of the blade holder 11. The clamp body 18 may be locked in placeby means of a respective screw 21 that is preferably embodied as adouble-thread screw. In the case shown here, the clamp body 18 serves tofix three blade holders 11 each having a planar face 20. Theconfiguration of the clamp body 18 and the triangular shape of theclamping faces 19 ensures an exact orientation of the blades 12 and theblade holder 11 at an angle of 120° to one another (see FIG. 1). Eachblade holder 11 may be axially displaced via a round wedge and theassociated screw 15. The bores 22 serve to orient the blade holders andtheir cutting edges parallel to the axis. A face 23 serves to ensurethat no line contact occurs between the blade holder 11 and the bore 22.As shown in FIG. 4, the blade holder 11 also has an angled face 24 whoseangle corresponds to the angle of the face 19 of the clamp body.

Alternately, instead of the snug bores, it is possible to use anexternal tension ring in conjunction with a clamp body positioned on theaxis, between which the blade holders 11 may be fixed. The tension ringis then screwed or shrunk onto the base body 10.

Details of the present invention are shown in particular by FIGS. 7, 9,and 10, which show enlarged views of the blades and/or the manufactureof the blades; FIG. 8 shows an optional embodiment in which inner andouter blade regions are angled back relative to a central blade region.

A bevel 29, which serves as a pre-wearing bevel, has the function ofemulating the wear pattern characteristic of the method while takinginto account the necessary blade bracing inward in a concave fashion.Thus, the tapered wear pattern is shortened. In a manner of speaking,one starts directly with the linear wear region. If no pre-wear bevelwere to be ground into the blade, taking into account the necessaryblade support running inward in a concave fashion, a deviation in shapewould occur already in the tapered wear region, thus ending the usefullife due to a shape deviation.

In order to obtain the blade shape according to the invention, the freeface of a blade 25, while maintaining the free angle, is either abradedin an inverted V-shape (with large radii and short cut lengths) or, asshown in FIG. 9, ground in a rounded convex fashion with a radius R,preferably approximately 900 mm.

The embodiment according to FIG. 9 results in a distance from a highestpoint 27 of the blade to the lowest point of 4 μm. If, in a secondprocess step, the bevel 29 is ground on a free face 28, with the camberangle of the blade being maintained, the illustrated embodiment of thebevel shown in FIG. 10 results, which has the largest width of 4 μmapproximately in the center of the blade 25. The bevel extends to theends of the cutting edge 25 or to a place ending shortly before theends, with the bevel 29 tapering out to be continuously narrower untilreaching a width of 0 mm at its two ends. The bevel thus results from achord-shaped cut through a roof-shaped or convex free face that is setat a free angle of 10°. The cutting angle is uniformly 0°. The blades 12are ground in a concave fashion at a camber angle of 90° or at aslightly smaller angle to the rotational axis of the tool, resulting inthe 4 μm elevation of the point 27. This way, instead of the wearpattern according to the curve 30 in FIG. 11 that results from the bladeholders known from prior art, a wear pattern 31 is achieved in which thelinear wear region has been considerably lengthened in that the taperedstarting wear region is shortened by a corresponding time.

In the alternate embodiment shown in FIG. 8, a lateral blade regionangled by 5° extends over a length a of 2 mm, the lateral blade regionbeing followed by a lateral blade region 25 b extending perpendicular toa longitudinal axis 26 running parallel to the rotational axis 13. Onthe inner side, a lateral blade region 25 c follows, which is alsoangled by 5°.

By the configuration of angled outer regions (twin capping) of a bladeprepared with a pre-wear bevel according to FIG. 8, which may beadditionally selected, the inner and outer cutting region isdeliberately removed from the cutting contact region. In the case of thetwo blades not provided with “twin capping,” a higher degree of freeface wear occurs in these regions. In the central cutting region where,by virtue of the method, the highest amount of free face region occurs,all three blades cut together. The wear behavior is used, so to speak,in favor of the required convex crankshaft bearing shape.

1. A blade holder for fixing in a milling head, comprising a shaft-likebar and a head with brazed-on blades, the blades having a lateralcutting edge formed by a cutting face and a free face, characterized bya bevel abutting the lateral cutting edge and formed on the free facewith a bevel width tapering down to
 0. 2. The blade holder according toclaim 1 wherein the bevel is positioned approximately central to thelateral cutting edge.
 3. The blade holder according to claim 1 whereinthe maximum width of the bevel ≦10 μm.
 4. The blade holder according toone of claims 1 wherein the bevel width continually decreases to 0 atboth ends or the bevel extends over the entire width of the lateralcutting edge.
 5. The blade holder according to one of claims 1 whereinthe bevel is produced using two consecutive grinding operations, namelya first grinding of the free face region adjacent the cutting edge to aconvex or roof shape and a subsequent partial surface grinding of thisfree face region.
 6. The blade holder according to claim 5 wherein theradius of the free face region ground in a convex fashion is R=900mm±100 mm.
 7. The blade holder according to one of claims 1 wherein thefree angle is 10°±2°.
 8. The blade holder according to claim 5, amultisection blade with a central blade region extending perpendicularto the longitudinal axis of the shaft, and with the blade regionsadjacent thereto being angled relative to the central blade region at anangle ≦10°.
 9. The blade holder according to claim 8 wherein the ratioof the length of the radially outer angled blade region to the centralblade region is 2:3 or the ratio of the length of the radially innerangled blade region to the radially outer lateral blade region is 2:1.10. A milling head with multiple blade holders inserted into seats of abase body, blades being soldered onto the blade holders, the bladeholders each being axially adjustable via a wedge and being fixable inthe milling head by means of clamping elements, characterized by twoblade holders according to claim 1 set at an equidistant angle to oneanother.